1. Field of the Invention
This invention relates to an apparatus for rapid burning of thermally pretreated, at least partially calcined fine grained products used in the manufacture of cement clinker. It includes a thermal reactor comprising a firing chamber with a flame therein as well as a means for introducing the product in concurrent flow with respect to the flame.
2. Description of the Prior Art
A standard industrial apparatus for cement manufacture comprises a suspension type heat exchanger wherein raw meal is heated in countercurrent flow with hot gases and is largely calcined upon an addition of fuel. The apparatus also includes a rotary tubular kiln wherein the thermally pretreated product is heated relatively slowly in a product bed up to its sintering temperature and then is heated and sintered up to clinker in countercurrent flow by means of flame gases from a burner.
It was long ago determined as illustrated in German Pat. No. 337,312 of May, 1921 that intimate contact between the flame and the product must occur in order to bring about a better and more efficient utilization of the flame gases.
One proposed solution consisted of a subdivided rotary tubular kiln having a sintering portion which rotated more slowly than its other portion, whereby the kiln for heating up to the sintering point circulated at such high speed that the product was lifted close to the apex of the kiln and fell freely down through the kiln cross section. This device, however, was never significantly commercialized due to the existence of excessive dust and wear.
It was perceived that it would be advantageous for reasons of energy and reaction kinetics to accomplish the heating in the temperature span between approximately 900.degree. C. after calcining of the raw meal and the finish-burning which occurs at approximately 1350.degree. through 1450.degree. C. with the highest possible heating gradients. This lead to a proposal as in East German Pat. No. 97,409 for a rapid burning wherein the powdery or agglomerated mixture was rapidly heated in a fluidized bed in a reactor, and sintered up to the finish-burning temperature. This Letters Patent suggests that it is very advantageous to burn fine grained product in the temperature range between approximately 1100.degree. and 1300.degree. C. with extremely high heating gradients. The advantage is said to be a reduction of the maturing time by about 70% with resulting advantages, for example, due to possible size reduction of the reactor or an increase in its throughput, or completing the finish-burning at lower temperatures with standard dwell times. Extremely high heating gradients in addition avoid deactivation of the product to be burned. This reference, however, does not contain a teaching as to providing an apparatus suitable for such rapid heating.